A Retractable Door to Reduce Drag on Fixed Gear Aircraft

The MarketAccording to a NASA study published in 1999, there were 160,577 General Aviation aircraft of which 75% had fixed gear. These airplanes have the obvious drag penalty of the gear remaining in the airstream while in flight, and while substantial drag reductions have been achieved with aerodynamic fairings and “wheel pants,” there is still an inherent drag penalty from the hole at the bottom where the tire must protrude.

The Problem This hole, while necessary for safe flight operations, allows air to circulate in and throughout the wheel pant creating a significant amount of turbulence and drag. The traditional solution is to seal the gaps between the wheel pants and the tire as closely as possible. While simple to execute, this solution greatly increases the risk of damage to the wheel pant when landing on unpaved runways and when encountering expansion joints on paved runways. Therefore, a marketable solution must balance safety, effectiveness and affordability.

The Design A door rotates around the tire on a rail system allowing uninhibited control of the aircraft on the ground while completely sealing the wheel pant from the airstream while in flight. The system is compatible with and mounts to the brackets and hardware of existing wheel pants, which makes installation easy and intuitive. Secondly, the system is composed of only three main parts (an inner bracket, an outer bracket, and the door). For fabrication, the aluminum brackets can be made at a machine shop and the doors can be made using additive manufacturing or traditional composite layups.

The actuator depends on the aircraft and pilot preference and includes: a manual push-pull cable, a hydraulic system, an electric servo motor, or through an automatic airspeed and differential pressure detectors. All of these methods would allow the door to be spring loaded such that the mechanism would fail in the open position. In the event a landing was made with the door in the closed position, the door would quickly break or wear away so that a controlled landing would be possible. And because the door is modular, (especially if additive manufacturing is used) a replacement would be easy to order.

Performance ResultsCFD testing of a single stock wheel pant from a RV-8 versus a modified wheel pant, at 225 mph, showed a 33% reduction in drag with only a marginal weight gain of 3 lbs (For an RV-8 this is a 2 mph increase in airspeed). In application, this means better cruise efficiency, which in turn leads to better fuel economy, shorter transit times, cheaper operation of the aircraft, and reduced carbon emissions. This is significant considering the simplicity and low weight of the system. And because of the low cost, it would be immediately marketable applicable to thousands of owners of fixed gear aircraft.

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ABOUT THE ENTRANT

Name: Thomas Lockwood

Type of entry: individual

Profession:Engineer/Designer

Thomas is inspired by:
I like to look at the inefficient things that we take for granted in everyday life and think about possible ways to make them better. It doesn’t always yield any practical solutions, but if we stop and decide that something can never be improved upon, then it won’t be.